This invention generally relates to engine-driven power supplies. More specifically, the invention relates to systems for controlling the supply of fuel to engines that drive power supplies.
Engine driven welding power supplies are well known, and may be driven either by a DC generator or an AC generator (also called an alternator-rectifier). An AC generator generally includes, in addition to an alternator, a reactor followed by rectifiers to provide a DC output. Electrical power produced by the generator as the engine drives rotation of the rotor is converted by known electrical components into useable welding power available at terminals.
Often, the output is controlled in welding power supplies using feedback. For example, a known field current control algorithm includes the steps of comparing field current to a set point and then adjusting the field current in response to deviations therefrom. Another prior art design receives welding current and/or welding voltage feedback, and controls the field current to produce a desired output. U.S. Pat. No. 5,734,147, issued Mar. 31, 1998 to the assignee of the present invention, and entitled Method and Apparatus for Electronically Controlling the Output of a Generator Driven Welding Power Supply, describes such a field current control. Another example of a known engine driven welding power supply with field current control can be operated to provide a constant current or constant voltage output.
Engine-driven welding power supplies of the foregoing type comprise a generator driven by an engine. Typically the engine is an internal combustion engine that burns gasoline. The engine is started either electrically (using a battery) or manually (by pulling a pull-start cable). Initially the engine may run at an idle speed, with the speed being increased to a running speed when a load is applied to the generator. For example, in one known system, the position of the governor arm of the engine can be changed by energizing a so-called xe2x80x9cidle solenoidxe2x80x9d, which is mechanically linked to the engine governor arm. The state of the idle solenoid is in turn controlled by a suitable idle control circuit that is part of the control system. The idle control circuit, in conjunction with other electrical components, senses the demand for welding power at the welding terminals and actuates the idle solenoid accordingly. During times when welding is taking place, the idle solenoid is de-energized. In the de-energized state, the plunger of the solenoid is free to float, and it does so as the governor arm changes its position to maintain a constant engine operating speed (e.g., 3,700 rpm). When the idle control circuit senses no demand for welding power at the terminals, it starts a delay routine. If after a predetermined period of time, no welding demand has been made, the idle control circuit actuates the solenoid, causing its plunger to retract. When the actuated solenoid clamps the governor arm, the engine speed drops to an idle speed (e.g., 2,200 rpm). However, the engine speed may be controlled in accordance with other control algorithms.
To turn off the welding machine, the engine must be turned off. In the case of an electric-start engine, the engine can be turned off by returning a start or ignition switch to its OFF position. In the case of a pull-start engine, the engine can be turned off by pressing a kill switch. In either case, it is desirable to cut off the supply of fuel in order to decrease fuel consumption and also to avoid after-bang in the muffler, caused when fuel passes through the engine cylinder(s) without being combusted and instead is combusted in the muffler. This circumstance arises when the engine receives fuel but does not receive ignition pulses.
A known device for cutting off the supply of fuel to a turned-off engine is a so-called xe2x80x9cfuel cutoff solenoidxe2x80x9d. U.S. Pat. No. 4,633,831 discloses a fuel cutoff system for a motor vehicle in which a control circuit activates a fuel cutoff solenoid in response to detection of a set of predetermined conditions. The fuel cutoff solenoid is adapted to operate a fuel cutoff valve placed in the fuel line that runs from the fuel tank to the engine. U.S. Pat. No. 6,166,525 discloses an automatic electric power generator control wherein the engine driving the generator stops at a predetermined time after the power demand is removed. In addition, a kill switch is provided to stop the engine. The ""525 Patent states that in the simplest case, the kill switch can be a switch or relay connected across the coil primary of the engine, thereby shorting the coil and eliminating the ignition spark; and further states that engines may also be stopped by a fuel shutoff solenoid valve, or a combination of the two methods.
There is a need for fuel shutdown systems and methods that cut off the supply of fuel when the engine of an engine-driven electric generator is turned off. Such systems are needed for both electric-start and pull-start internal combustion engines.
The invention is directed to methods and systems for cutting off the supply of fuel to an engine in response to engine turn-off. The invention is particularly directed to methods and systems wherein a fuel cutoff solenoid or functionally equivalent device is connected to a source of electrical power in response to detection of conditions representing engine turn-off.
One aspect of the invention is a method for cutting off the supply of fuel to an engine, comprising the steps of detecting whether ignition pulses are present; and activating a device for cutting off the supply of fuel to the engine in response to detection of a change from a first state in which ignition pulses are present to a second state in which ignition pulses are absent. The device may be activated by drawing electrical power from a battery or from a stator winding in an electric generator being driven by the engine.
Another aspect of the invention is a system for cutting off the supply of fuel to an engine, comprising: a battery power supply; a first device that cuts off the supply of fuel to the engine when energized by the battery power supply and does not cut off the supply of fuel to the engine when not energized by the battery power supply; a second device for connecting the first device to the battery power supply in a first state and disconnecting the first device from the battery power supply in a second state; and a control circuit that causes a change of state of the second device from the second state to the first state in response to a change from ignition pulses being present to ignition pulses being absent. In one disclosed embodiment, the first device is a solenoid and the second device is a relay.
A further aspect of the invention is a method for cutting off the supply of fuel to an engine being used to drive an electric generator, comprising the following steps: detecting whether ignition pulses are present; and coupling a rotor winding of the generator to ground and a stator winding of the generator to a fuel cutoff device in response to detection of cessation of ignition pulses.
Another aspect of the invention is a power generation system comprising: an engine, an engine ignition controller for providing ignition pulses to the engine, a stator winding or coil for providing a generator output, a rotor winding driven to rotate by the engine, and a fuel shutdown system for cutting off the supply of fuel to the engine. The fuel shutdown system comprises: a first device that cuts off the supply of fuel to the engine when energized by the battery power supply and does not cut off the supply of fuel to the engine when not energized by the battery power supply; a second device having first and second states, the rotor winding being connected to ground when the second device is in its first state and not connected to ground when the second device is in its second state; a third device having first and second states, the stator winding or coil being connected to the first device when the third device is in its first state and not connected to the first device when the third device is in its second state; and a control circuit that causes a first change of state of the second device from its second state to its first state and a second change of state of the third device from its second state to its first state in response to cessation of ignition pulses. In one disclosed embodiment, the first device is a solenoid and the second and third devices are relays.
Yet another aspect of the invention is a method for cutting off the supply of fuel to an engine being used to drive an electric generator, comprising the following steps: detecting whether the engine has been turned off; and connecting an input of fuel cutoff device to an output of a stator winding of the generator in response to detection of engine turn-off, the fuel cutoff device being energized by the generator output.
Other aspects of the invention are disclosed and claimed below.